The growth mechanisms of imogolite-like aluminogermanate nanotubes have been examined at various stages of their formation. The accurate determination of the nucleation stage was examined using a combination of local- (XAS at the Ge−K edge and 27Al NMR) and semilocal scale technique (in situ SAXS). For the first time, a model is proposed for the precursors of the nanotubular structure and consist in rooftile-shaped particles, up to 5 nm in size, with ca. 26% of Ge vacancies and varying curvatures. These precursors assemble to form short nanotubes/nanorings observed during the aging process. The final products are most probably obtained by an edge−edge assembly of these short nanotube segments.

Greenhouse-grown root, foliage, fruit, and seed crops were exposed to peroxyacetyl nitrate (PAN) at 0, 5, 10, 20, and 40 ppb, 4 hours per day, twice per week, from germination to maturity of harvestable product. A response of PAN dose and growth or yield parameters was significant only for lettuce (Lactuca sativa L. cv. Empire) and Swiss chard (Beta vulgaris L. var. cicla, cv. Fordhook). Leaf fresh weight was reduced by 13% in ‘Empire’ lettuce and by 23% in chard in the 40 ppb PAN treatments relative to 0 ppb PAN controls. Peroxyacetyl nitrate at 10 ppb appeared to stimulate the growth of most crops. The threshold for inhibition of growth by PAN, under conditions of 2 exposures per week, appeared to be between 10 and 20 ppb. These results suggest that PAN, at concentrations below the threshold for visible injury, can alter the growth of plants, but that significant reductions in growth or yield may occur only in highly susceptible cultivars of leafy crops.